The United States, as well as many other countries, has an abundant source of unconventional Oil and Gas resources located in shale formations. Hence, the term Shale Oil or Shale Gas. However, these tight shale formations require a unique completion method, referred to as hydraulically fracturing, to untrap the oil and/or gas and allow it to flow to the production tubing of the well. In order to keep the fractures open, the well must be propped open with a high strength material. This is similar to propping a door open with a wooden wedge or divider. However, in lieu of wooden wedge or dividers high strength material, such as frac sand and/or ceramic beads, are pumped into the well and into the fissures formed from hydraulically fracturing the well. Proppants are used to “prop” open the oil or gas well during hydraulic fracturing of the well. Hence the term “proppant.”
Frac sand is traditionally used as the proppant for most hydraulically fractured wells. However, the crush strength and spherical shape of frac sand is far inferior to that of ceramic proppants. Many Oil and Gas operators have turned to ceramic proppants to improve the conductivity or flow of the well after it has been hydraulically fractured. Due to the inherit superior spherical shape of ceramic proppants over frac sand, conductivity (flow) of ceramic proppants allows for enhanced gas and/or oil flow within the well. This is crucial for maximizing flow from the well.
Carbo Ceramics, Inc. manufactures an extensive line of proppants that range from resin-coated sand to ceramic proppants. For example, US Patent Application Publication No. US 2012/20231981 A1, which is hereby incorporated by reference in its entirety, describes various processes for manufacturing proppant particles.
The major issues associated with the manufacture of ceramic proppants are cost, production capacity and emissions. The traditional method for sintering ceramic proppants uses long rotary kilns fired with natural gas. First, the construction and installation of a new rotary kiln is expensive and requires a long lead-time (e.g., upwards of 18 to 24 months), so capacity expansion is difficult. Second, if the price of natural gas increases the production costs increase. On the other hand, when the price of natural gas decreases, operators tend to not drill gas wells and/or use frac sand. As a result, sales decrease for ceramic proppants. Third, many facilities utilizing rotary kilns must install expensive scrubbers to reduce air emissions. Other issues associated with long rotary kilns are size, footprint, plant location and regulatory permits. The combination of these problems causes long lead times and thus hampers a company's ability to increase production capacity to keep up with demand of high performance ceramic proppants as compared and contrasted to frac sand.
In addition, sintering time within a rotary kiln is exceptionally long in order to reach a typical sintering temperature of 2,800° F. to 3,000° F. Typical sintering times range from 30 minutes to over one hour. If temperature creeps beyond the sintering temperature, the lower melting point metals and/or minerals within the green proppant tend to melt and “plate” out within the kiln. Thus, the rotary kiln must be shutdown, cooled and repaired and of course adversely affects the plants production capacity.
Due to the abundance of natural gas and oil from shale plays, there exists an need for an alternative means for sintering proppants without using long rotary kilns.